establishing the level of development (lod

ESTABLISHING THE LEVEL OF DEVELOPMENT (LOD) REQUIREMENTS FOR MODELING IN HIGHWAY INFRASTRUCTURE PROJECTS Bharathwaj Sankaran1 and William J. O’Brien2 1) Graduate Student, Department of Civil Architectural and Environmental Engineering, The University of Texas at Austin, TX, USA. Email: [email protected] 2) Ph.D., P.E., Associate Professor, Department of Civil Architectural and Environmental Engineering, The University of Texas at Austin, TX, USA. Email: [email protected]

Abstract: Delivering infrastructure projects through model-based workflow is becoming more common in recent years. Understanding the degree of information required for the elements in the model plays a significant role in ensuring its utilization for the intended purpose. Existing definitions of Level of Development (LOD) have helped the building industry to formalize and communicate this vital requirement among major project stakeholders. Although there can be lessons learned from the current literature for LOD in the context of Building Information Models (BIM), the unique characteristics of transportation infrastructure projects necessitate formulation of guidelines adapted to meet their modeling requirements. This paper proposes specifications for LOD in highway projects based on the objectives of modeling. A review of projects is conducted to understand the various applications for which models are developed and used in highway projects. The proposed guidelines are validated with specific examples of projects, demonstrating their practical utility. A modeling matrix is also proposed to guide the LOD documentation process for applying these recommendations in practice. The findings of this study will assist practitioners in standardizing the LOD definitions for highway projects and serve as a foundation for future research in this area. Keywords:

Model-based workflow, BIM, Level of Development (LOD).

1. INTRODUCTION As per the National Building Information Modeling Standard Committee, a Building Information Model (BIM) is ―a digital representation of physical and functional characteristics of a facility‖. The information embedded in the model can be utilized to support different decisions taken during the lifecycle of the facility (NBIMS, 2014). Over the past few decades, the building construction industry have applied BIM positively for a wide range of applications entailing cost estimating, scheduling, constructability analyses, design coordination and clash detection, among others. The broadening capabilities of the modeling tools coupled with ever-increasing computational power and mobility of computers is enabling the transition to an integrated digital project delivery process (Construction, 2014). The facets of issues surrounding deployment of models by building industry have been investigated by various academicians and practitioners. Resources exist in literature that have demonstrated through case studies the benefits, challenges, opportunities and risks involved in integrating BIM with project work processes (Azhar, 2011, Barlish & Sullivan, 2012). Adopting model-driven approach to highway infrastructure projects is relatively new in comparison to the building sector. Some of the unique characteristics of transportation projects that makes a model-based workflow challenging are the following: large horizontal footprint, major earthwork operations and associated uncertainties in precisely modeling the cut and fill volumes, higher coordination with external stakeholders for tasks such as Right of Way (ROW) acquisition, utilities coordination and relocation, and public information (Liapi, 2003). However, evidences suggest that workflow of these projects are equally aligned well to stand benefitted through the application of BIM. Hartmann et al. (2008) reported that the 3-D model-based photorealistic animations had assisted the governmental agencies in the early planning stage of a project for gathering public and political support. O’Brien et al. (2012) had positively evaluated the value offered by 3-D models towards assisting Right of Way (ROW) acquisition planning, constructability reviews, utility conflicts resolution through clash detection, and work zone management through case studies of projects in Dallas, Texas. Kim et al. (2011) used 4-D CAD models in a case study of a cable-stayed bridge to illustrate its benefits in the areas of materials management, temporary construction and work space management. Unlike building projects, highway infrastructure projects have to be effectively coordinated with movement of traffic. Presence of construction work zone on highways can cause delays due to congestion and regulated speed limits in the area. They lead to safety risks for both the commuters and construction workers (FHWA, 2006). Thus, it would be beneficial if the 3-D model used for visualization in highway projects also include elements of traffic control measures, apart from the design information related to the facility. Hughes (2004) identified the future needs of visualization with 3-D models as centerpiece. He illustrated that the future visualization tools should possess adequate capabilities to demonstrate not only how the facility looks but also how it would operate. Wei & Jarboe (2010) integrated realistic 3-D traffic simulation models with design 3-D CAD models to generate advanced visualization to be used for communication among various stakeholders,

including the project team and public. The aforementioned evidences suggest that 3-D models generated for highway projects might have multiple components synchronized with each other – 3-D design models, traffic simulation models. Also the linear nature of the projects may also require terrain to be accurately modeled in 3-D for these projects (such as Digital Terrain Models (DTMs)). In line with these stated differences, it becomes necessary to define and understand the LOD specifications as they apply for highway infrastructure projects. The rest of the paper is organized as follows: the next section provides background research on LOD and its significance as reported for BIM implementation. The ―research objective and methodology‖ section briefly describes the approach adopted to collect data and proposes LOD specifications for highway projects. In the next section, examples of actual projects are also provided to illustrate its validity. Finally, the ―conclusion‖ section summarizes the findings and enlists recommendations for future work. 2. BACKGROUND RESEARCH ON LOD A critical issue which often impacts the modeling process is ascertaining the LOD to be incorporated in the models. American Institute of Architects (AIA) defines Level of Development in BIM as ―minimum dimensional, spatial, quantitative, qualitative, and other data included in a Model element to support the authorized uses associated with such LOD‖(AIA, 2013a. p.2). It had provided LOD specifications for modeling various building components. Also prescribed were instructions regarding authorized uses of the models corresponding to each LODs (AIA, 2013b). Establishing the LOD requirements for the entities in the model is critical for successful BIM integration with project work processes. BIMForum, (2014) outlined the significance of LOD specifications as follows: it helps project teams in clearly articulating and specifying the elements to be included in the BIM deliverables, it assists in communicating the design intent among the project team to ensure all the members are well aligned with respect to BIM requirements, and it also serves as a protocol that can be incorporated in contract documents and BIM execution plans. Many organizations have incorporated the contract specifications for LOD and/or developed their own customized ways to monitor and report the LOD during the project development. U.S. Army Corps of Engineers (USACE) had developed a Minimum Modeling Matrix (M3) for this purpose. An interactive spreadsheet based tool, it provides instructions on recording LOD for each elements in the model, classified by disciplines responsible for creating and maintaining the respective elements (Structural, architectural, mechanical, and plumbing.). Such a matrix would ensure clarity and consistency regarding information exchange between all the project stakeholders and avoid any potential conflicts. It would also help ascertain the authorities who is responsible for maintaining the stipulated LOD, as defined formally by contract or any other agreed mechanism (USACE, 2014). Other organizations that have similar guidelines for LOD specifications include the General Services Administration (GSA), AIA and UK BIM protocol group, among many other agencies. Transportation agencies, such as Departments of Transportation (DOTs) in the U.S., have also recognized the potential benefits offered by utilizing 3-D models for several domain-specific applications such as earthwork quantity computations, Automated Machine Guidance (AMG) during construction, and stringless paving of concrete/asphalt pavements (FHWA, 2013). To support the widespread implementation of 3-D models, it is imperative to establish the LOD specifications for highway projects. This step would enable standardized modeling practices across several project participants including owners, contractors and other service providers. 3. RESEARCH OBJECTIVE AND METHODOLOGY The objective of the paper is to develop recommendations for LOD specific to the modeling needs of highway infrastructure projects. The study will also extract the lessons learned and consider the overlapping points with the existing recommendations from agencies such as USACE, AIA and UK BIM group, among others. To achieve the proposed objective, an extensive literature review was performed to synthesize the different categories of 3-D models developed and used on highway projects. Academic sources (such as journals, conference proceedings, book chapters) and practitioners’ supporting documents (such as the U.S Federal Highway Administration’s documents, projects’ engineering reports and modeling related documents) were both considered to produce balanced observations. Data was also collected from 3-D models developed for various transportation projects in Texas by interviewing project engineers from Texas DOT (TxDOT). The findings are discussed next. 3.1 Categories Of Models In Highway Projects The various 3-D models developed for highway projects can be grouped under the three main categories – Surface models, Structure models and traffic models. Surface models include the elements that are highly dependent on terrain (surface) elevations for specifications concerning the design development. Roadway corridors, curbs and gutter drainage systems typically fall under this category. Modeling these elements follows the standard highway design process – hierarchically working through Triangular Irregular Network (TIN) surface, alignments, offset alignments,

profiles, cross-sectional assemblies and corridors - that rely extensively on the surface-related data for design and modeling. The 3-D surface models are widely being used for AMG during construction. Hence, the surface models need to be designed for construction specifications as they are directly used to perform various construction operations. The general process followed here is conversion of the required 3-D design related information – namely horizontal and vertical alignments for the project, proposed surface, existing surface, control points, breaklines etc. - to the required file format ( Ex: LandXML) to be used as an input for machine guidance on the field. The Structure models include all the other structural elements of highway projects such as bridges, underground utilities and retaining walls, among others. It has to be noted that existing LOD guidelines for BIM can be applied to many of the entities present in the structure models of highways. These categories of models are developed for various applications such as design visualization, spatial and temporal conflicts identification, constructability analysis and public information. The traffic models consist of modeling the traffic control elements put in place to coordinate the work zone (such as crash barriers, barrels, Variable Message Sign boards, Intelligent Transportation Systems and so on). Also some projects have utilized 3-D traffic microsimulation and other advanced tools to visualize and analyze the impacts of proposed work zone measures on traffic (such as travel time across work zone, queuing delay, congestion, and safety assessment). Such models have also benefitted the public information. 3.2 Factors Impacting LOD On Highway Projects Before determining the specifications, it is important to understand the driving factors that will play a role in determining the LOD for elements of highway projects. Although there is no strict correspondence between these factors and a particular LOD, a qualitative evaluation would be beneficial. These factors are broadly categorized into two types – Supply-side constraints and demand-based requirements. Table 1 enumerates the identified factors under the two categories. Table 1. Categories of factors impacting LOD on projects Supply-side constraints Data availability (D) IT infrastructure – Hardware and software (I) Resources availability (R)

Demand-based requirements Project’s current Timeline (P) Objective of modeling (O)

The factors are explained further with examples pertaining to highway projects. These factors would often work in combination to determine the appropriate LOD. (The acronyms mentioned in brackets are used in Table 4) (1) Supply-side Constraints This includes the list of factors that impose restrictions on the LOD of the model due to limiting constraints in the project development process. Thus the agencies should work towards improving or resolving the supply-side constraints. Non-availability (or low quality) of information concerning project elements can often reduce the apparent benefits in the modeling process. Creators/users of the model will then have to deal with reduced LOD to account for uncertainty in the available input information. Examining the factor of data availability early on in the modeling process would help understand and propose the pertinent remedial measures to improve its efficiency and resolve this constraint. As an example, in the transportation projects, one of the most frequently reported challenges is accurately locating the underground utilities for modeling them in 3-D. Recognizing this constraint would help make informed decisions in resolving it during the modeling process (In this case, on whether to collect more information on depth of the utilities or to refrain from modeling them). Another supply-side issue that can impact the LOD in the modeling process is availability of supporting IT infrastructure – hardware, software and other technological tools. The agencies that have understood and invested in the software tools, computers and associated information systems – either in-house or through outsourcing – will have this constraint resolved. Resource availability is a major constraint that affects the LOD of the model. This includes constraints such as cost, staffing availability, time and effort required for modeling. Availability of funding and skilled manpower can help in producing models with higher LOD. Also, available time to create the model often dictates the LOD. Khwaja and Schmeits (2014) reported that the timeframe available for creating the model was an important factor impacting the LOD. Finally, the modeling effort needs to be considered (number of elements and labor-hours required) while allocating resources for creating the model (Leite, et al., 2011). (2) Demand Requirements It refers to the factors that are drivers (as opposed to constraints) to create the models with the desired LOD. Project’s current timeline (phase) plays an important role in the LOD evolution process (Bedrick

2008). The information required for creating greater LOD models will generally tend to evolve and become available as the project moves through subsequent phases. As an example, detailed design information will be required for modeling roadways and bridges. However the data remains unavailable until the project moves on to the design stage. Similarly, utilities may not be required to be modeled until it can be integrated with detailed design data to perform the required tasks such as 3-D model-based clash detection. The objective of the model (or its intended application on the project) is the primary factor in determining the appropriate LOD. There exists a plethora of applications for 3-D models. However, each application would require models with different LOD. As an example, 3-D models specifically meant for contractor’s AMG will require high LOD for surface elements (such as surfaces of lanes, curbs, gutters, datum points, stakeout points for bridges, Retaining walls) in comparison to structure elements (actual bridges, utilities) and traffic elements. Many agencies produce 3-D models that fall under this category as they can be used for construction automation. On the other hand, models developed for advanced visualization to be understood by diverse stakeholders on the project will have to include greater LOD for surface, structure and traffic elements. Many agencies have developed these kinds of models for executing complex projects, where stakeholders’ communication and public participation is crucial for the project’s success. Complex bridges, roundabouts and interchange projects typically require creation of visualization model preferably with high LOD for all the elements involved. 3.3 LOD Specifications Development Tables 2 synthesizes the discussions on factors affecting LOD and provide structured guidelines for ascertaining LOD based on the model objective. The ―model category‖ is used to represent the increasing level of development from 0 to 3. It is an index used to convey the holistic maturity of all the constituent models developed for the project – namely surface, structure and traffic. Table 2. Guidelines for ascertaining LOD Model objective AMG in the field Public Information (PI) and stakeholder communication Design/Constructability reviews, clash detection Advanced visualization

Desired level of development (LOD) Surface Structure Traffic elements elements elements High Low-Medium Low Medium Medium Medium high Medium High Medium High

High

High

Model Category 0 1 2 3

There were suggestions, both in the literature and from the data collected from TxDOT, that the intended application of the model is the primary factor that often determines its LOD in highway projects. Hence the specifications in Table 2 are mapped to corresponding objectives of modeling. The three major divisions of LOD for each categories of model – low, medium and high – were also determined based on the model objectives and are explained further in Table 3. They represent increasing degree of information for the respective constituent models (i.e. Surface, structure or traffic). In Table 2, recommendations for some constituent models possess multiple propositions. As an example, it is recommended here that models developed for PI purposes could possess the elements of traffic models with medium to high LOD. Although it is desirable to model the actual traffic conditions for PI, there may be constraints due to non-availability of resources (data, time, and budget) that often limits the extent of traffic modeling on projects. Presence of such constraints is the primary reason behind a range of suggestions for LOD, rather than a single value. BIMForum (2013) provided guidelines for ascertaining LOD for underground utilities and site improvement measures. The specifications proposed herein can also be used in conjunction with these existing LOD guidelines for the structure models. The correspondence between the BIM LOD and specifications proposed here are as follows: ―low‖ category implies ―LOD 100‖, ―medium‖ represents ―LOD 200‖, and ―high‖ would mean ‖LOD 300‖.

Table 3. Guidance table for choosing the degree of information

Element type Surface

Structures

Traffic

Others

Low Basic representation of roadway elements (lanes, curbs and other assemblies) and basic representation of non-roadway surface elements (Existing Ground, Proposed Ground, Digital Terrain Models) Basic geometry of bridges, utilities, retaining walls and other structures. (equivalent to LOD 100) Basic representation of elements of TCPs and basic/no 3-D traffic simulation

Medium Approximate representation of roadway elements ( Lane with cross slopes, curbs, and other cross sectional elements) and ) approximate representation of non-roadway elements Approximate geometry of bridges, utilities, retaining walls and other structures. (equivalent to LOD 200) Approximate representation of elements of TCPs and basic 3-D traffic simulation

Nil

Include information on surrounding buildings, any other ROW elements

High Accurate representation of roadway and non-roadway elements with AMG quality; Add visualization components such as raster imagery

Accurate geometry of bridges, utilities, retaining walls and other structures (equivalent to LOD 300) Accurate representation of elements of TCPs and representation of expected traffic conditions using methods such as 3-D traffic simulation vetted with field counts. Include information on buildings, any other ROW elements.

4. DEMONSTRATION OF PRACTICAL APPLICATION The specifications proposed in this paper would assist in formalizing the concept of LOD for highway projects and will serve as a basis for future research and refinement in this area. It can also act as a standard language for communication among project participants in the issues concerning model elements. The practical utility of these LOD classifications is illustrated in this section with project examples drawn from TxDOT. Many agencies across the world had utilized 3-D DTM surface models and machine control files that have been used on many of their highway projects specifically for the purpose of AMG. These detailed surface models with limited details on structures and traffic elements are designated under ―0‖ category. A schematic representation of this category of model is shown in Figure 1. It typically consists of break lines, control lines, datum points, terrain model of the proposed conditions such as corridors and retaining walls.

Figure 1. Pictorial representation of a 3-D DTM Surface model (Category ―0‖) A category ―1‖ model should include reasonable information (―medium‖ LOD) regarding the terrain and structures of the project. The public would be more interested in understanding the work zone measures and lane

configurations in place and hence it should possess ―high‖ LOD for traffic elements. In the LBJ expressway project, that involves reconstruction of 16.5 mile portion of Interstate-635 (I-635) and I-35 East, a category ―1‖ 3-D model was developed and utilized to communicate the elements of Traffic Control Plans (TCPs) to the public. The PI strategy with the 3-D model helped in better visualization and communication of the construction activities, lane closures and detour configurations. A pictorial representation of the model developed for this project is as shown in Figure 2 (Khwaja and Schmeits., 2014).

Figure 2. 3D model communicating lane closures and construction activities (Category 1) In an another instance, the President George Bush Turnpike (PGBT) project of Dallas, Texas that involved construction of an interchange connecting I-30 and the PGBT utilized 3-D and 4-D modeling to perform constructability reviews. The interchange, ROW elements and the utilities were modeled in 3-D to facilitate the process of clash detection between design entities. Availability of good quality data facilitated modeling of utilities (storm and sanitary sewers) and drill shafts of the foundation to perform clash detection in 3-D. This helped in identifying and resolving many spatial conflicts between the design elements in the project, thereby avoiding the costly conflicts that could have occurred during the construction phase (O’Brien et al., 2012). This model was developed with high level of detail for surface and structure elements. The details included for traffic elements are relatively less. Thus, these models can be classified under ―2‖ category. A thematic representation of this category of models is shown below in Figure 3.

Figure 3. (Left) Perspective of the 3-D model of the PGBT project, (Right) Utilities modeled for clash detection process (Category ―2‖)

Wisconsin DOT’s South East freeway projects (such as the Zoo Interchange) that is under construction aims to produce advanced visualization to improve the project delivery processes and enhance communication process among the project stakeholders. Driven by the agency’s requirements, they are not only performing detailed modeling for terrain and structures but are also utilizing traffic microsimulation tools (e.g., PTV VISSIM tool) to model and assess the impact of proposed traffic control measures (Parve, 2012).. Thus, these models that possess high LOD for all the design entities fall under the category ―3‖. 4.1 Using LOD In Practice - A Modeling Matrix For Highway Projects As noted by BIMForum (2013), it may be inappropriate to call a model as belonging to ―LOD __‖ at its entirety, since project models are bound to contain constituent elements at varying levels of development. So, a systematic way of monitoring and reporting LOD of different project elements is paramount for applying these recommendations in practice. Parve (2014) used a Project Modeling Matrix to guide the LOD documentation process on highway projects. Following these observations, a representative modeling matrix was developed and shown in Table 4 based on the knowledge from existing literature and incorporating additional improvements. The values in the matrix are provided for demonstration purpose and they do not reflect actual observations on any project. Each of the major project elements (surface, structures or traffic) in Table 4 can further be subdivided into its associated sub-entities depending on the reporting needs and modeling requirements of a project. The various other attributes, apart from LOD, also carry significant information related to modeling and are hence provided to maintain integrity and completeness in the LOD documentation process. Table 4. A representative modeling matrix for highway projects Major Project Elements

Format

n-D

LOD

Work area

Factors

DGN

LoA (feet) 0.01

R/W and Environmental areas Non-roadway surfaces Roadway features and surfaces Drainage-storm sewer Bridges (all elements) Retaining walls Signature bridges (Steel) Other structures Proposed special foundations Proposed special foundation walls Lighting Intelligent Transportation Systems Signs Traffic Signal Proposed water main Proposed sanitary sewer Existing utilities Traffic simulations

2-D

medium

Surveying

R

DGN DGN DGN DGN DGN DWG DWG DWG DWG DWG DGN DGN DGN DGN DGN DGN VISSIM

0.01 0.01 0.05 0.03 0.05 0.01 0.05 0.02 0.05 0.01 0.01 0.05 0.01 0.01 0.05 0.01 -

3-D 3-D 3-D 3-D 2-D 3-D 2-D 3-D 2-D 3-D 3-D 3-D 3-D 3-D 3-D 2-D 3-D

high high high high medium high low medium medium high high high high medium high low medium

Design Design Design Bridges Design Design Various Design Design Utilities Traffic Traffic Traffic Utilities Utilities Utilities Traffic

O O O O R P I O R O O O O R,D O R,D O

The attributes of Table 4 are described below (1) Format: It refers to the format of files containing the particular element (DWG/DGN/XML/VISSIM) (2) LoA: It describes the level of accuracy of location data used for modeling the elements (Ex: 0.01’) (3) n-D: It describes the maximum dimension of the element being modeled (Ex: 2-D, 3-D, 4D referring to adding schedule data, 5-D referring to adding cost data and so on). (4) LOD: It describes the level of development of the element being modeled (Low, medium, high). (5) Work area: It identifies the departments responsible for ensuring development of the respective model elements (e.g., Surveying, Design, Construction, Traffic , Operations & Maintenance) (6) Factors: It refers to the main driving factor that could have an impact in maintaining suitable LOD 5. CONCLUSION Although lagging behind the building industry, the transportation sector have also started incorporating 3-D models in project delivery processes for various applications. Understanding and standardizing the LOD documentation process is important to reap the full benefits of these semantically rich information models and to

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